Galvanized anchor bolts and embrittlement 1

[Eabrar]

Hi dears!

Currently i m involved in a project of steel structure with pile foundations. Total load on foundations is 350 Tons.

Anchor bolts of material ASTM A307 are to be fixed in concerete fundations. These bolts are ugently requirement of my project otherwise whole project may delay. Zinc plated (Hot dip) anchor bolts are offered by the lowest bidder. But according to ASTM A143 and A153 embrittlement is enhanced in cold bent rods of dia greater than 7mm after galvanizing. Thermal treatment (upto 600 deg C)before galvanizing should be employed to cater this problem. Vendor in my case has not employed any heat treatment. My queries are as follows:

1. Is embrittlement a serious concern in my case (dias of 36mm, 42mm and 20mm)?
2. Which anchor bolts you people prefer in this kind of projects, whether galvanized or simple?
3. Any other solution which you can offer?

Your earliest reply is required.

 

[rob768]

I think embrittlement can be a problem in high strength steels due to hydrogne pick-up in the pickling proces prior to galvanizing. I am not sure, but annealing may solve this problem?

 

[Eabrar]

Thanks Rob for ur valuable reply.

If u can search more information, it will be a great help!

 

[WillisV]

This problem has been addressed before - do a keyword search for anchor embrittlement.

 

[SlideRuleEra]

About 15 years ago we had a long series of discussions with our consultants about hot dip galvanizing (or alternatives) of anchor bolts (all sizes, up to 100 mm diameter) at a planned electric generating station. Over the 65 years that some plants have been in operation have never had a problem with embrittlement. However corrosion has caused numerous failures (even WITH hot dip galvanizing). We always required fabrication of anchor bolts before being hot dipped.

The bottom line, for our company, was (and still is) that the hot dip protection is worth the risk of embrittlement.

The American Galvanizers Association has information on "Bend Diameters for Steel to be Galvanized" at

http://www.galvanizeit.org/content/index.cfm?fuseaction=showContent&contentID=151&navID=193

and "Considerations for Steel Cold-worked Prior to Galvanizing" at

http://www.galvanizeit.org/content/index.cfm?fuseaction=showContent&contentID=154&navID=196

http://www.SlideRuleEra.net

 

[Kwan]

I looked up the limit for baking off hydrogen in ferrous metals (in my aero references). I found that anything less than 160 ksi does not require either stress relief bakes or embittlement bakes.

This is a good thread to send to the metal and metallurgy forum. They can give you direction with this issue.

 

[Rich2001]

Watch both the Acid & Alkaline rinses, temperature concentrations etc. many galvanizer have very little in way of process control.

The presence of low-melting-point elements such as tin and bismuth in the galvanizing melt have a role in causing LME (Liquid Metal Embrittlement) or as known in the EU LMAC (Liquid Metal Assisted Cracking). However, the relative significance of melt composition in the galvanizing bath on the potential for steel cracking is not fully understood. More research is required.

Always obtain a copy of the galvanization bath chemical analysis and look at the tin, bismuth, and lead levels. If the % tin (wt) + % lead (wt) is greater than 1.3% (by weight) or the % bismuth (wt) is greater than 0.1% (by weight), a closer examination for cracking is warranted, preferably with dry AC yoke MT.

While not directly answering your question, the following items do provide additional information.

"Galvanizing Structural Steelwork - An approach to the management of Liquid Metal Assisted Cracking"

http://www.steelconstruction.org/st...ssionID=-1136569656781&entityName=publication

"Current Knowledge of the Cracking of Steels During Galvanizing"

http://www.aisc.org/Template.cfm?Se...Management/ContentDisplay.cfm&ContentID=30636

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